1. Field of the Invention
The present invention relates to transceivers, and, more particularly, to a radio frequency identification tag reader used in an RFID (Radio Frequency Identification) system.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2007-228254 and Japanese Unexamined Patent Application Publication No. 2006-238282 disclose radio frequency identification tag readers.
Japanese Unexamined Patent Application Publication No. 2007-228254 discloses a radio frequency identification tag reader including a circulator with which an antenna is shared for transmission and reception.
FIG. 1 is an overall schematic view of a radio frequency identification tag communication system disclosed in Japanese Unexamined Patent Application Publication No. 2007-228254. Referring to FIG. 1, a radio frequency identification tag communication system S includes an interrogator 100 and radio frequency identification tags T that are transponders for the interrogator 100. The radio frequency identification tag T includes a radio frequency identification tag circuit element To including an antenna 51 and an IC circuit 52. The interrogator 100 includes an antenna 1 for transmitting/receiving a signal to/from the antenna 51 included in the radio frequency identification tag circuit element To by radio communication, a high-frequency circuit 2 for accessing the IC circuit 52 included in the radio frequency identification tag circuit element To via the antenna 1 (performing reading or writing on the IC circuit 52), a signal processing circuit 3 for processing a signal read from the radio frequency identification tag circuit element To, and a control circuit 4.
Japanese Unexamined Patent Application Publication No. 2006-238282 discloses a radio frequency identification tag reader that uses different antennas (a transmission antenna and a receiving antenna) for transmission and reception.
However, when a circulator is used as disclosed in Japanese Unexamined Patent Application Publication No. 2007-228254, a transceiver is increased in size. On the other hand, when a transmission antenna and a receiving antenna are separately provided as disclosed in Japanese Unexamined Patent Application Publication No. 2006-238282, a predetermined spacing between these antennas is required to achieve the isolation between them and a transceiver is increased in size.